This application is based upon and claims the benefit of priority from the prior Japanese Patent Application No. 2001-183792, filed Jun. 18, 2001, the entire contents of which are incorporated herein by reference.
1. Field of the Invention
The present invention relates to a damper mechanism used for an automobile steering device.
2. Description of the Related Art
An automobile steering device includes a steering shaft rotating integrally with a steering wheel, a steering column rotatably supporting the steering shaft, and a shaft assembly transferring the rotation of the steering shaft to the steering gear side. Also, it is known in the art to provide steering devices equipped with a damper mechanism (elastic shaft coupling), commonly referred to as a steering damper, in order to prevent the transfer of micro-vibrations generated on a wheel side to the steering wheel side.
Conventional damper mechanisms include an outer pipe, an inner member inserted into the outer pipe, and a rubber-like elastic body mounted between the outer pipe and the inner member, as disclosed in Japanese Patent Laid-Open No. 9-72347 and No. 5-116636.
In the damper mechanism, the micro-vibrations transferred from the steering gear side is absorbed in the range in which the elastic body can be deformed. When the steering wheel is rotated for steering, the outer pipe and the inner member are relatively displaced in the twisting direction. As long as the displacement (twist angle) is small, the elastic body is deformed in the direction of twisting (shearing direction). When an input exceeding a predetermined twist angle is applied, a stopper operates, and thus torque is transferred between the outer pipe and the inner member.
In the conventional damper mechanisms, the elastic body is subjected to a shearing force. Therefore, problems arise with durability if the elastic body is made of rubber. When the spring constant of the elastic body is decreased to improve the absorptive property of the micro-vibrations transferred from the steering gear side, problems arise in steering performance in the range of a normal steering angle (when the steering wheel is handled). However, when the spring constant of the elastic body is set high, the micro-vibrations transferred from the steering gear side cannot be absorbed sufficiently.
Accordingly, it is an object of the present invention to provide a damper mechanism for a steering device capable of effectively absorbing microvibrations transferred from the steering gear side and improving steering performance in the range of a normal steering angle.
A damper mechanism according to the present invention includes an outer pipe, an inner member, and an elastic body. Inward convex portions and concave grooves extending along the axial direction are alternately formed in the circumferential direction at a plurality of positions of the inner periphery of the outer pipe. Outward convex portions extending along the axial direction are formed in the circumferential direction at a plurality of positions of the outer periphery of the inner member. The elastic body is provided between the outer pipe and the inner member.
In the damper mechanism of the invention, in the range of a minute twist angle, the elastic body is deformed in the direction of compression between the inward convex portions of the outer pipe and the outward convex portions of the inner member, thereby absorbing micro-vibrations. In the range of a normal steering angle, the inward convex portions are brought into engagement with the outward convex portions and both of them rotate integrally, thereby transferring torque.
In this invention, preferably, the elastic body includes a thick wall portion provided between one side of the outward convex portion of the inner member and a first inward convex portion of the outer pipe and a thin wall portion provided between the other side of the outward convex portion and a second inward convex portion, thereby increasing the spring constant with an increase in the twist angle. More preferably, a clearance is held between the thin wall portion and the second inward convex portion. The clearance allows the outer pipe and the inner member to be relatively displaced at a minute angle in the twisting direction.
Additional objects and advantages of the invention will be set forth in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. The objects and advantages of the invention may be realized and obtained by means of the instrumentalities and combinations particularly pointed out hereinafter.